单项选择题 Strainers, sometimes called （）, are devices designed to prevent the passage of unwanted solids into or further along a system.

单项选择题 A(n) （） is a special type of valve which prevents the passage of steam but allows condensate to pass.

单项选择题 Fuel oil tanks must be fitted with （） that can be closed rapidly and remotely in the event of an emergency such as a fire.